Vertical plasma processing apparatus and method for semiconductor process

ABSTRACT

A vertical plasma processing apparatus for a semiconductor process includes a process container having a process field configured to accommodate a plurality of target substrates at intervals in a vertical direction, and a marginal space out of the process field. In processing the target substrates, a control section simultaneously performs supply of a process gas to the process field from a process gas supply circuit and supply of a blocking gas to the marginal space from a blocking gas supply circuit to inhibit the process gas from flowing into the marginal space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional Application of, and claims the benefitof priority under 35 U.S.C. § 120 from, U.S. application Ser. No.11/696,501, filed Apr. 4, 2007, which claims the benefit of priorityunder 35 U.S.C. § 119 from prior Japanese Patent Applications No.2006-104730, filed Apr. 5, 2006 and No. 2006-116021, filed Apr. 19,2006. The entire contents of each of the above applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vertical plasma processing apparatusand method for a semiconductor process, such as a vertical plasma filmformation apparatus and method for forming a thin film, such as asilicon-containing insulating film, on a target substrate, such as asemiconductor wafer. The term “semiconductor process” used hereinincludes various kinds of processes which are performed to manufacture asemiconductor device or a structure having wiring layers, electrodes,and the like to be connected to a semiconductor device, on a targetsubstrate, such as a semiconductor wafer or a glass substrate used foran FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), byforming semiconductor layers, insulating layers, and conductive layersin predetermined patterns on the target substrate.

2. Description of the Related Art

In manufacturing semiconductor devices for constituting semiconductorintegrated circuits, a target substrate, such as a semiconductor wafer(made of, e.g., silicon) is subjected to various processes, such as filmformation, etching, oxidation, diffusion, reformation, annealing, andnatural oxide film removal. US 2003/0224618 A1 discloses a semiconductorprocessing method of this kind performed in a vertical heat-processingapparatus (of the so-called batch type). According to this method,semiconductor wafers are first transferred from a wafer cassette onto avertical wafer boat and supported thereon at intervals in the verticaldirection. The wafer cassette can store, e.g., 25 wafers, while thewafer boat can support 30 to 150 wafers. Then, the wafer boat is loadedinto a process container from below, and the process container isairtightly closed. Then, a predetermined heat process is performed,while the process conditions, such as process gas flow rates, processpressures, and process temperatures, are controlled.

In recent years, owing to the demands of increased miniaturization andintegration of semiconductor integrated circuits, it is required toalleviate the thermal history of semiconductor devices in manufacturingsteps, thereby improving the characteristics of the devices. Forvertical processing apparatuses, it is also required to improvesemiconductor processing methods in accordance with the demandsdescribed above. For example, there is a CVD (Chemical Vapor Deposition)method for a film formation process, which performs film formation whileintermittently supplying a source gas and so forth to repeatedly formlayers each having an atomic or molecular level thickness, one by one,or several by several (for example, Jpn. Pat. Appln. KOKAI PublicationsNo. 6-45256 and No. 11-87341). In general, this film formation method iscalled ALD (Atomic layer Deposition), which allows a predeterminedprocess to be performed without exposing wafers to a very hightemperature.

Further, WO 2004/066377 (Dec. 15, 2004), which corresponds to U.S. Pat.No. 7,094,708 B2, discloses a structure of a vertical processingapparatus for performing ALD, which utilizes plasma assistance tofurther decrease the process temperature. According to this apparatus,for example, where dichlorosilane (DCS) and NH₃ are used as a silanefamily gas and a nitriding gas, respectively, to form a silicon nitridefilm (SiN), the process is performed, as follows. Specifically, DCS andNH₃ gas are alternately and intermittently supplied into a processcontainer with purge periods interposed therebetween. When NH₃ gas issupplied, an RF (radio frequency) is applied to generate plasma so as topromote a nitridation reaction. More specifically, when DCS is suppliedinto the process container, a layer with a thickness of one molecule ormore of DCS is adsorbed onto the surface of wafers. The superfluous DCSis removed during the purge period. Then, NH₃ is supplied and plasma isgenerated, thereby performing low temperature nitridation to form asilicon nitride film. These sequential steps are repeated to complete afilm having a predetermined thickness.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a vertical plasmaprocessing apparatus and method for a semiconductor process, which canimprove the process gas usage rate and process throughput withoutadversely affecting the process field.

Another object of the present invention is to provide a vertical plasmaprocessing apparatus and method for a semiconductor process, which canimprove the planar uniformity and/or inter-substrate uniformity of aplasma process performed on a target substrate.

According to a first aspect of the present invention, there is provideda vertical plasma processing apparatus for a semiconductor process, theapparatus comprising:

a process container having a process field configured to accommodate aplurality of target substrates at intervals in a vertical direction, anda marginal space out of the process field;

a support member configured to support the target substrates inside theprocess field;

an exciting mechanism including a plasma generation area disposed in aspace communicating with the process field, the plasma generation areaextending over a length corresponding to the process field in a verticaldirection;

a process gas supply circuit configured to supply a process gas to theprocess field, such that the process gas is exited while passing throughthe plasma generation area, and the process gas is supplied to theprocess field to form essentially horizontal gas flows;

an exhaust system configured to exhaust gas from the process field, andincluding an exhaust port facing the plasma generation area with theprocess field interposed therebetween;

a blocking gas supply circuit configured to supply a blocking gas to themarginal space, such that the blocking gas is not supplied directly tothe process field but is supplied directly to the marginal space; and

a control section configured to control an operation of the apparatus,wherein, in processing the target substrates, the control sectionsimultaneously performs supply of the process gas to the process fieldfrom the process gas supply circuit and supply of the blocking gas tothe marginal space from the blocking gas supply circuit to inhibit theprocess gas from flowing into the marginal space.

According to a second aspect of the present invention, there is provideda processing method in a vertical plasma processing apparatus for asemiconductor process,

the apparatus including

a process container having a process field configured to accommodate aplurality of target substrates at intervals in a vertical direction, anda marginal space out of the process field,

a support member configured to support the target substrates inside theprocess field,

an exciting mechanism including a plasma generation area disposed in aspace communicating with the process field, the plasma generation areaextending over a length corresponding to the process field in a verticaldirection,

a process gas supply circuit configured to supply a process gas to theprocess field, such that the process gas is exited while passing throughthe plasma generation area, and the process gas is supplied to theprocess field to form essentially horizontal gas flows,

an exhaust system configured to exhaust gas from the process field, andincluding an exhaust port facing the plasma generation area with theprocess field interposed therebetween, and

a blocking gas supply circuit configured to supply a blocking gas to themarginal space, such that the blocking gas is not supplied directly tothe process field but is supplied directly to the marginal space,

the method comprising: processing the target substrates whilesimultaneously performing supply of the process gas to the process fieldfrom the process gas supply circuit and supply of the blocking gas tothe marginal space from the blocking gas supply circuit to inhibit theprocess gas from flowing into the marginal space.

According to a third aspect of the present invention, there is provideda vertical plasma processing apparatus for a semiconductor process, theapparatus comprising:

a process container having a process field configured to accommodate aplurality of target substrates at intervals in a vertical direction, anda marginal space out of the process field;

a support member configured to support the target substrates inside theprocess field;

a heater configured to heat the target substrates inside the processfield;

an exciting mechanism including a plasma generation area disposed in aspace communicating with the process field, the plasma generation areaextending over a length corresponding to the process field in a verticaldirection;

a process gas supply system configured to selectively supply into theprocess field a first process gas that provides a main material of athin film and a second process gas that reacts with the first processgas, so as to deposit the thin film on the target substrates, such thatat least one of the first and second process gases is exited whilepassing through the plasma generation area, and the first and secondprocess gases are supplied to the process field to form essentiallyhorizontal gas flows;

an exhaust system configured to exhaust gas from the process field, andincluding an exhaust port facing the plasma generation area with theprocess field interposed therebetween;

a blocking gas supply circuit configured to supply a blocking gas to themarginal space, such that the blocking gas is not supplied directly tothe process field but is supplied directly to the marginal space; and

a control section configured to control an operation of the apparatus,wherein, in order to deposit the thin film on the target substrates, thecontrol section executes supply of the first process gas to the processfield and supply of the second process gas to the process field,repeatedly a plurality of times, while simultaneously performing supplyof each of the first and second process gases to the process field fromthe process gas supply system and supply of the blocking gas to themarginal space from the blocking gas supply circuit to inhibit the firstand second process gases from flowing into the marginal space.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a sectional view showing a vertical plasma processingapparatus (vertical plasma film formation apparatus) according to afirst embodiment of the present invention;

FIG. 2 is a sectional plan view showing part of the apparatus shown inFIG. 1;

FIG. 3 is a timing chart of the gas supply of a film formation methodaccording to the first embodiment of the present invention;

FIG. 4 is a view showing an apparatus (comparative example) used in anexperiment wherein no blocking gas is supplied into a lower space S1;

FIG. 5 is a view showing an apparatus (present example) used in anexperiment wherein a blocking gas is supplied into a lower space S1;

FIG. 6 is a graph showing the relationship between the position on awafer and the film thickness obtained by the apparatus shown in FIG. 4in Experiment 1;

FIG. 7 is a graph showing the relationship between the position on awafer and the film thickness obtained by the apparatus shown in FIG. 5in Experiment 1;

FIG. 8 is a graph showing the relationship between the position on awafer and the film thickness obtained by the apparatus shown in FIG. 5in Experiment 2;

FIG. 9 is a graph showing the relationship between the position on awafer and the film thickness obtained by the apparatus shown in FIG. 5in Experiment 3;

FIG. 10 is a sectional view showing a vertical plasma processingapparatus (vertical plasma film formation apparatus) according to asecond embodiment of the present invention; and

FIG. 11 is a sectional view showing a vertical plasma processingapparatus (vertical plasma film formation apparatus) according to athird embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the process of developing the present invention, the inventorsstudied problems caused in vertical plasma processing apparatuses, asthose disclosed in WO 2004/066377 and so forth. As a result, theinventors have arrived at the findings given below.

In general, the process container of a vertical plasma processingapparatus has a marginal space out of a process field configured toaccommodate a plurality of wafers at intervals in the verticaldirection. In the case of the apparatus disclosed in WO 2004/066377, themarginal space comprises a lower space and an upper space respectivelypresent below and above the process field. The lower space and upperspace respectively correspond to a space below the bottom plate of awafer boat for supporting wafers and a space above the top platethereof. During a process, a process gas is supplied and exhaustedessentially uniformly in the horizontal direction, so as to form gasflows parallel with the wafers. Even so, part of the process gas flowsinto the lower space and upper space and stays there, and then isexhausted without making a contribution to the process reaction.

Where part of the process gas stays in the marginal space, it isnecessary to prolong the purge period (vacuum-exhaust time) for removingthis gas part. In this case, the process throughput is decreased to alarge extent, particularly in a processing method of the ALD typedescribed above, in which process gas supply periods and purge periodsare alternately repeated. Further, where part of the process gas flowsinto the marginal space, useless consumption of the process gas, whichis relatively expensive, is increased, and the running cost is therebyincreased to a large extent. In addition, as described later, where partof the process gas flows into the marginal space, the process gascreates local flows, which deteriorate the planar uniformity and/orinter-substrate uniformity of the plasma process on wafers.

Embodiments of the present invention achieved on the basis of thefindings given above will now be described with reference to theaccompanying drawings. In the following description, the constituentelements having substantially the same function and arrangement aredenoted by the same reference numerals, and a repetitive descriptionwill be made only when necessary.

First Embodiment

FIG. 1 is a sectional view showing a vertical plasma processingapparatus (vertical plasma film formation apparatus) according to afirst embodiment of the present invention. FIG. 2 is a sectional planview showing part of the apparatus shown in FIG. 1. The film formationapparatus 2 has a process field configured to be selectively suppliedwith a first process gas containing dichlorosilane (DCS) gas as a silanefamily gas, a second process gas containing ammonia (NH₃) gas as anitriding gas, and a purge gas comprising an inactive gas, such as N₂gas. The film formation apparatus 2 is configured to form a siliconnitride film on target substrates by CVD in the process field.

The apparatus 2 includes a process container 4 shaped as a cylindricalcolumn with a ceiling and an opened bottom, in which a process field 5is defined to accommodate and process a plurality of semiconductorwafers (target substrates) stacked at intervals. The process container 4further includes a marginal space out of the process field 5, whichcomprises a lower space S1 and an upper space S2 respectively presentbelow and above the process field 5, in this embodiment.

The entirety of the process container 4 is made of, e.g., quartz. Thetop of the process container 4 is provided with a quartz ceiling plate 6to airtightly seal the top. The bottom of the process container 4 isconnected through a seal member 10, such as an O-ring, to a cylindricalmanifold 8. The process container may be entirely formed of acylindrical quartz column without a manifold 8 separately formed.

The cylindrical manifold 8 is made of, e.g., stainless steel, andsupports the bottom of the process container 4. A wafer boat 12 made ofquartz is moved up and down through the bottom port of the manifold 8,so that the wafer boat 12 is loaded/unloaded into and from the processcontainer 4. The wafer boat 12 includes a bottom plate 12 a and a topplate 12 b between which a number of target substrates or semiconductorwafers W are stacked. For example, in this embodiment, the wafer boat 12has struts 12A that can support, e.g., about 50 to 100 wafers having adiameter of 300 mm at essentially regular intervals in the verticaldirection.

The wafer boat 12 is placed on a table 16 through a heat-insulatingcylinder 14 made of quartz. The table 16 is supported by a rotary shaft20, which penetrates a lid 18 made of, e.g., stainless steel, and isused for opening/closing the bottom port of the manifold 8. In a statewhere the wafer boat 12 is set in position within the process field 5,as described above, the lower space S1 and upper space S2 of themarginal space respectively correspond to a space below the bottom plate12 a of the wafer boat 12 and a space above the top plate 12 b thereof.

The portion of the lid 18 where the rotary shaft 20 penetrates isprovided with, e.g., a magnetic-fluid seal 22, so that the rotary shaft20 is rotatably supported in an airtightly sealed state. A seal member24, such as an O-ring, is interposed between the periphery of the lid 18and the bottom of the manifold 8, so that the interior of the processcontainer 4 can be kept sealed.

The rotary shaft 20 is attached at the distal end of an arm 26 supportedby an elevating mechanism 25, such as a boat elevator. The elevatingmechanism 25 moves the wafer boat 12 and lid 18 up and down in unison.The table 16 may be fixed to the lid 18, so that wafers W are processedwithout rotation of the wafer boat 12.

A gas supply section is connected to the side of the manifold 8 tosupply predetermined process gases to the process field 5 within theprocess container 4. Specifically, the gas supply section includes asecond process gas supply circuit 28, a first process gas supply circuit30, and a blocking gas supply circuit 32. The first process gas supplycircuit 30 is arranged to supply a first process gas containing a silanefamily gas, such as DCS (dichlorosilane) gas. The second process gassupply circuit 28 is arranged to supply a second process gas containinga nitriding gas, such as ammonia (NH₃) gas. Each of the first and secondprocess gas supply circuits 30 and 28 is further arranged to supply aninactive gas alone, such as N₂ gas, as a purge gas. The blocking gassupply circuit 32 is arranged to supply an inactive gas, such as N₂ gas,as a blocking gas (used as a purge gas, as well). In place of N₂ gas,the inactive gas may be another inactive gas, such as He gas, Ar gas, orNe gas. Each of the first and second process gases may be mixed with asuitable amount of carrier gas, as needed. However, such a carrier gaswill not be mentioned, hereinafter, for the sake of simplicity ofexplanation.

More specifically, the second process gas supply circuit 28 and firstprocess gas supply circuit 30 include gas distribution nozzles 34 and36, respectively, each of which is formed of a quartz pipe whichpenetrates the sidewall of the manifold 8 from the outside and thenturns and extends upward (see FIG. 1). The gas distribution nozzles 34and 36 respectively have a plurality of gas spouting holes 34A and 36A,each set being formed at predetermined intervals in the longitudinaldirection (the vertical direction) over all the wafers W on the waferboat 12. The blocking gas supply circuit 32 includes a short gas nozzle38, which penetrates the sidewall of the manifold 8 from the outside.The gas nozzle 38 has a gas spouting holes 38A opened within the lowerspace S1 below the bottom plate 12 a of the wafer boat 12, in which theheat-insulating cylinder 24 and table 26 are present.

The nozzles 34, 36, and 38 are connected to gas sources 28S, 30S, and32S of NH₃ gas, DCS gas, and N₂ gas, respectively, through gas supplylines (gas passages) 42, 44, and 46, respectively. The gas supply lines42, 44, and 46 are provided with switching valves 42A, 44A, and 46A andflow rate controllers 42B, 44B, and 46B, such as mass flow controllers,respectively. With this arrangement, NH₃ gas, DCS gas, and N₂ gas can besupplied at controlled flow rates.

A gas exciting section 50 is formed at the sidewall of the processcontainer 4 in the vertical direction. On the side of the processcontainer 4 opposite to the gas exciting section 50, a long and thinexhaust port 52 for vacuum-exhausting the inner atmosphere is formed bycutting the sidewall of the process container 4 in, e.g., the verticaldirection.

Specifically, the gas exciting section 50 has a vertically long and thinopening formed by cutting a predetermined width of the sidewall of theprocess container 4, in the vertical direction. The opening is closed bya partition plate 54 having a gas passage 55 and is covered with aquartz cover 56 airtightly connected to the outer surface of the processcontainer 4. The cover 56 has a vertically long and thin shape with aconcave cross-section, so that it projects outward from the processcontainer 4. The process container 4, the partition plate 54, and thecover 56 of the gas exciting section 50 are made of the same insulativematerial (specifically, quartz), and are connected to each other bywelding. The partition plate 54 is fixed to the wall defining theopening formed in the process container 4 while the cover 56 is fixed tothe outer surface of the process container 4.

With this arrangement, the gas exciting section 50 is formed such thatit projects outward from the sidewall of the process container 4 and isconnected on the other side to the interior of the process container 4.In other words, the inner space of the gas exciting section 50communicates through the gas passage 55 of the partition plate 54 withthe process field 5 within the process container 4. The partition plate54 has a vertical length sufficient to cover all the wafers W on thewafer boat 12 in the vertical direction.

A pair of long and thin electrodes 58 are disposed on the opposite outersurfaces of the cover 56, and face each other while extending in thelongitudinal direction (the vertical direction). The electrodes 58 areconnected to an RF (Radio Frequency) power supply 60 for plasmageneration, through feed lines 62. An RF voltage of, e.g., 13.56 MHz isapplied to the electrodes 58 to form an RF electric field for excitingplasma between the electrodes 58. The frequency of the RF voltage is notlimited to 13.56 MHz, and it may be set at another frequency, e.g., 400kHz.

The gas distribution nozzle 34 of the second process gas is bent outwardin the radial direction of the process container 4 and penetrates thepartition plate 54, at a position lower than the lowermost wafer W onthe wafer boat 12. Then, the gas distribution nozzle 34 verticallyextends at the deepest position (the farthest position from the centerof the process container 4) in the gas exciting section 50. As alsoshown in FIG. 2, the gas distribution nozzle 34 is separated outwardfrom an area sandwiched between the pair of electrodes 58 (a positionwhere the RF electric field is most intense), i.e., a plasma generationarea PS where the main plasma is actually generated. The second processgas containing NH₃ gas is spouted from the gas spouting holes 34A of thegas distribution nozzle 34 toward the plasma generation area PS. Then,the second process gas is excited (decomposed or activated) in theplasma generation area PS, and is supplied in this state through the gaspassage 55 of the partition plate 54 onto the wafers W on the wafer boat12.

An insulating protection cover 64 made of, e.g., quartz is attached toand covers the outer surface of the cover 56. A cooling mechanism (notshown) is disposed in the insulating protection cover 64 and comprisescoolant passages respectively facing the electrodes 58. The coolantpassages are supplied with a coolant, such as cooled nitrogen gas, tocool the electrodes 58. The insulating protection cover 64 is coveredwith a shield (not shown) disposed on the outer surface to prevent RFleakage.

The gas distribution nozzle 36 of the first process gas extends upwardat a position near and outside the partition plate 54 of the gasexciting section 50, i.e., outside the gas exciting section 50 (insidethe process container 4). The first process gas containing DCS gas isspouted from the gas spouting holes 36A of the gas distribution nozzle36 toward the center of the process container 4. The gas spouting holes36A are formed at positions between the wafers W on the wafer boat 12 todeliver the first process gas (containing DCS) essentially uniformly inthe horizontal direction, so as to form gas flows parallel with thewafers W.

The partition plate 54 has a gas passage 55 formed therein for theplasma generation area SP to communicate with the process field 5. Thegas passage 55 consists of a number of gas diffusion holes 55A having acircular shape. The gas diffusion holes 55A are arrayed in one verticalrow at predetermined intervals in the longitudinal direction (thevertical direction) of the partition plate 54 over all the wafers W onthe wafer boat 12. The gas diffusion holes 55A are formed at positionsbetween the wafers W on the wafer boat 12, at the same regular intervalsas the intervals of the wafers W. The gas diffusion holes 55A allow thesecond process gas (containing NH₃) activated by plasma to passtherethrough essentially uniformly in the horizontal direction, so as toform gas flows parallel with the wafers W.

The partition plate 54 decreases the gas flow conductance between theplasma generation area SP and process field 5. Consequently, thepressure of the plasma generation area SP can be increased withoutadversely affecting the process field 5 in terms of pressure. It followsthat the plasma generation efficiency can be improved, and the wallsurface defining the gas exciting section 50 is less sputtered by plasmaions.

On the other hand, the exhaust port 52, which is formed opposite the gasexciting section 50, is covered with an exhaust port cover member 66.The exhaust port cover member 66 is made of quartz with a U-shapecross-section, and attached by welding. The exhaust port cover member 66extends upward along the sidewall of the process container 4, and has agas outlet 68 at the top of the process container 4. The gas outlet 68is connected to a vacuum-exhaust system GE including a vacuum pump andso forth. The vacuum exhaust system GE has an exhaust passage 84connected to the gas outlet 68, on which a valve unit (an opening degreeadjustment valve) 86, a vacuum pump 88, and a detoxification unit 89 forremoving undesirable substances are disposed in this order from theupstream side.

The process container 4 is surrounded by a heater 70, which is used forheating the atmosphere within the process container 4 and the wafers W.A thermocouple (not shown) is disposed near the exhaust port 52 in theprocess container 4 to control the heater 70.

The film formation apparatus 2 further includes a main control section48 formed of, e.g., a computer, to control the entire apparatus. Themain control section 48 can control the film formation process describedbelow in accordance with the process recipe of the film formationprocess concerning, e.g., the film thickness and composition of a filmto be formed, stored in the memory thereof in advance. In the memory,the relationship between the process gas flow rates and the thicknessand composition of the film is also stored as control data in advance.Accordingly, the main control section 48 can control the elevatingmechanism 25, gas supply circuits 28, 30, and 32, exhaust system GE(including the valve unit 86), gas exciting section 50, heater 70, andso forth, based on the stored process recipe and control data.

Next, an explanation will be given of a film formation method (so calledALD (Atomic Layer Deposition) film formation) performed in the apparatusshown in FIG. 1. In summary, this film formation method is arranged toselectively supply a first process gas containing dichlorosilane (DCS)gas as a silane family gas and a second process gas containing ammonia(NH₃) gas as a nitriding gas to the process field 5 accommodating wafersW to form a silicon nitride film on the wafers W by CVD.

At first, the wafer boat 12 at room temperature, which supports a numberof, e.g., 50 to 100, wafers having a diameter of 300 mm, is loaded intothe process container 4 heated at a predetermined temperature. Then, theinterior of the process container 4 is vacuum-exhausted and kept at apredetermined process pressure, and the wafer temperature is increasedto a process temperature for film formation. At this time, the apparatusis in a waiting state until the temperature becomes stable. Then, thefirst process gas containing DCS gas and the second process gascontaining NH₃ gas are intermittently supplied from the respective gasdistribution nozzles 36 and 34 at controlled flow rates. Further, theblocking gas or purge gas consisting of N₂ gas is supplied from the gasnozzle 38 in a manner described below.

Specifically, the first process gas containing DCS gas is supplied fromthe gas spouting holes 36A of the gas distribution nozzle 36 to form gasflows parallel with the wafers W on the wafer boat 12. While beingsupplied, molecules of DCS gas and molecules and atoms of decompositionproducts generated by its decomposition are adsorbed on the wafers W.

On the other hand, the second process gas containing NH₃ gas is suppliedfrom the gas spouting holes 34A of the gas distribution nozzle 34 toform horizontal gas flows toward the partition plate 54. The secondprocess gas is selectively excited and partly turned into plasma when itpasses through the plasma generation area PS between the pair ofelectrodes 58. At this time, for example, radicals (activated species),such as N*, NH*, NH₂*, and NH₃*, are produced (the symbol ┌*┘ denotesthat it is a radical). The radicals flow out from the gas passage 55 ofthe partition plate 54 of the gas exciting section 50 toward the centerof the process container 4, and are supplied into gaps between thewafers W in a laminar flow state.

The radicals react with molecules of DCS gas adsorbed on the surface ofthe wafers W, so that a silicon nitride film is formed on the wafers W.Alternatively, when DCS gas flows onto radicals adsorbed on the surfaceof the wafers W, the same reaction is caused, so a silicon nitride filmis formed on the wafers W.

When each of the first process gas and second process gas is supplied tothe process field 5, the blocking gas consisting of an inactive gas issimultaneously supplied to the lower space S1, which belongs to themarginal space, from the gas spouting hole 38A of the gas nozzle 38.Consequently, each of the first process gas and second process gas isinhibited from flowing into the lower space S1, thereby improving theprocess throughput, the process gas usage rate, and the planaruniformity and/or inter-substrate uniformity of the process.

Specifically, where the blocking gas is supplied to the lower space S1,not only each of the first process gas and second process gas isinhibited from flowing into the lower space S1, but also the process gashaving flowed thereinto can be swiftly exhausted. Consequently, it ispossible to shorten the time necessary for removing the process gas,thereby improving the throughput. Further, since the process gas isinhibited from flowing into the lower space S1 by the blocking gas,useless consumption of the process gas, which is relatively expensive,is decreased. Consequently, it is possible to improve the process gasusage rate and to decrease the running cost. Furthermore, since theprocess gas is inhibited from flowing into the lower space S1, theprocess gas can flow more uniformly relative to the surface of thewafers. Consequently, it is possible to improve the planar uniformityand/or inter-substrate uniformity of the process.

FIG. 3 is a timing chart of the gas supply of a film formation methodaccording to the first embodiment of the present invention. In thisembodiment, the blocking gas also serves as a purge gas, and this gasmay be supplied in a manner selected from various manners describedlater. In FIG. 3, (A) and (B) respectively show supply of the firstprocess gas (denoted as DCS in FIG. 3) and second process gas (denotedas NH₃ in FIG. 3) to the process field 5. Further, (C1) to (C6) showssix different examples of supply of the blocking gas (denoted as N₂ inFIG. 3) to the lower space S1.

As shown in FIG. 3, the film formation method according to thisembodiment is arranged to alternately repeat first to fourth steps T1 toT4. A cycle comprising the first to fourth steps T1 to T4 is repeated anumber of times, and thin films of silicon nitride formed by respectivecycles are laminated, thereby arriving at a silicon nitride film havinga target thickness. At first, a process adopting a first example (C1) ofsupply of the blocking gas will be explained.

The first step T1 is arranged to perform supply of the first process gasto the process field 5, while stopping supply of the second process gasto the process field 5. The second step T2 is arranged to stop supply ofthe first and second process gases to the process field 5. The thirdstep T3 is arranged to perform supply of the second process gas to theprocess field 5, while stopping supply of the first process gas to theprocess field 5. Further, in the third step T3, the RF power supply 60is set in the ON state to turn the second process gas into plasma by thegas exciting section 50, so as to supply the second process gas in anactivated state to the process field 5. The fourth step T4 is arrangedto stop supply of the first and second process gases to the processfield 5. According to the first example (C1), supply of the blocking gasto the lower space S1 is continuously performed over the entirety of thefirst step to fourth step at the same flow rate. Further, preferably,the process field 5 is continuously vacuum-exhausted by the vacuumexhaust system GE through the exhaust passage 84 over the entirety ofthe first step T1 to the fourth step T4.

Each of the second and fourth steps T2 and T4 is used as a purge step toremove the residual gas within the process container 4. The term “purge”means removal of the residual gas within the process container 4 byvacuum-exhausting the interior of the process container 4 whilesupplying an inactive gas, such as N₂ gas, into the process container 4(this corresponds to the first example (C1)), or by vacuum-exhaustingthe interior of the process container 4 while stopping supply of all thegases. In this respect, the second and fourth steps T2 and T4 may bearranged such that the first half utilizes only vacuum-exhaust and thesecond half utilizes both vacuum-exhaust and inactive gas supply.Further, the first and third steps T1 and T3 may be arranged to stopvacuum-exhausting the process container 4 while supplying each of thefirst and second process gases. However, where supplying each of thefirst and second process gases is performed along with vacuum-exhaustingthe process container 4, the interior of the process container 4 can becontinuously vacuum-exhausted over the entirety of the first to fourthsteps T1 to T4.

The first step T1 is set to be within a range of about 1 to 120 seconds,e.g., at about 5 seconds. The second step T2 is set to be within a rangeof about 1 to 30 seconds, e.g., at about 5 seconds. The third step T3 isset to be within a range of about 1 to 120 seconds, e.g., at about 10seconds. The fourth step T4 is set to be within a range of about 1 to 30seconds, e.g., at about 5 seconds. In general, the film thicknessobtained by one cycle of the first to fourth steps T1 to T4 is about0.05 to 0.11 nm. Accordingly, for example, where the target filmthickness is 50 nm, the cycle is repeated about 500 times. However,these values of time and thickness are mere examples and thus are notlimiting.

As described above, where the blocking gas is supplied to the lowerspace S1, not only each of the first process gas and second process gasis inhibited from flowing into the lower space S1, but also the processgas having flowed thereinto can be swiftly exhausted. For example, it isassumed that a film formation process is arranged to repeat 500 times acycle comprising the first to fourth steps T1 to T4. In this case, ifthe gas purge operation of each cycle is shortened by a few seconds,such as 2 seconds, the total film formation time can be shortened by1,000 seconds (=2×500), thereby improving the throughput.

The flow rate of DCS gas is set to be within a range of 50 to 2,000sccm, e.g., at 1,000 sccm (1 slm: standard liter per minute). The flowrate of NH₃ gas is set to be within a range of 100 to 5,000 sccm, e.g.,at 3,000 sccm. The flow rate of N₂ gas is set to be within a range of 10to 30,000 sccm, e.g., at 5,000 sccm. The process temperature is lowerthan that for ordinary CVD processes, and is set to be within a range of250 to 700° C., and preferably of 350 to 600° C. If the processtemperature is lower than 250° C., essentially no film is depositedbecause hardly any reaction is caused. If the process temperature ishigher than 700° C., a low quality CVD film is deposited, and existingfilms, such as a metal film, may suffer thermal damage.

The process pressure (the pressure of the process field 5) is set to bewithin a range of 0.2 to 1 Torr (27 to 133 Pa (1 Torr=133.3 Pa)). Thiscondition can improve the planar uniformity and inter-substrateuniformity in the thickness of a film formed by the plasma filmformation. If the process pressure is higher than 1.0 Torr, radicals aredeactivated drastically. If the process pressure is lower than 0.2 Torr,the film formation rate becomes lower than the practical level.

On the other hand, the pressure of the plasma generation area SP (thepressure inside the gas exciting section 50) is set to be within a rangeof, e.g., 0.7 to 5.0 Torr (93 to 667 Pa). If the pressure of the plasmageneration area SP is set higher, the plasma generation efficiency canbe improved, so the plasma density becomes higher. If the pressure ofthe plasma generation area SP is higher than 5.0 Torr, the plasmaignition becomes very difficult. If this pressure is lower than 0.7Torr, the plasma generation efficiency is deteriorated drastically.

FIG. 3 also shows second to sixth examples (C2) to (C6) of supply of theblocking gas different from the first example (C1). However, the mannerof supply of the blocking gas is not limited to these examples, and itmay be selected from other various manners.

In the second example (C2), each of the second and fourth steps T2 andT4 is arranged to completely stop supply of the blocking gas in thelatter half period Lt. Consequently, exhaust of the residual gas withinthe process container 4 is facilitated. In the third example (C3), eachof the second and fourth steps T2 and T4 is arranged to completely stopsupply of the blocking gas over the entirety thereof. In this case,consumption of the blocking gas is decreased by that much correspondingto stoppage of supply of the blocking gas. In the fourth example (C4),the flow rate of the blocking gas is set in accordance with the flowrates of the first and second process gases, such that it is smallerwhen the first process gas is supplied and is larger when the secondprocess gas is supplied. Further, each of the second and fourth steps T2and T4 is arranged to completely stop supply of the blocking gas overthe entirety thereof. In the fifth example (C5), the flow rate of theblocking gas is set in reverse of the fourth example (C4), such that itis larger when the first process gas is supplied and is smaller when thesecond process gas is supplied. In the sixth example (C6), the flow rateof the blocking gas is varied stepwise in one cycle of the first tofourth steps T1 to T4, such that it reaches the peak when the secondprocess gas is supplied.

Also in these modifications, each of the first process gas and secondprocess gas is inhibited from flowing into the lower space S1, therebyimproving the process throughput, the process gas usage rate, and theplanar uniformity and/or inter-substrate uniformity of the process.

Experiment 1

A comparative experiment was performed between an apparatus (comparativeexample) shown in FIG. 4 with no blocking gas supplied into the lowerspace S1 and an apparatus (present example) shown in FIG. 5 with theblocking gas supplied into the lower space S1. In FIGS. 4 and 5, thepartition plate 54 is not shown. In this experiment, wafers having adiameter of 200 mm were used as target substrates. The first process gascontaining DCS gas was set at a flow rate of 100 sccm. The secondprocess gas containing NH₃ gas was set at a flow rate of 500 sccm. Inthe apparatus shown in FIG. 5, supply of the blocking gas wascontinuously performed in accordance with the first example (C1) shownin FIG. 3. The N₂ used as the blocking gas was set at a flow rate of 1slm. Under these conditions, a film formation process was performed byrepeating 500 times a cycle comprising the first to fourth steps T1 toT4 shown in FIG. 3.

FIGS. 6 and 7 are graphs showing the relationship between the positionon a wafer and the film thickness obtained by the apparatuses shown inFIGS. 4 and 5, respectively, in Experiment 1. In FIGS. 6 and 7, thehorizontal axis denotes the position (mm) on a wafer, and the verticalaxis denotes the film thickness (nm). No. 5, No. 31, and No. 57 in FIGS.6 and 7 denote the number of a wafer of 61 wafers supported on the waferboat 12, which were counted from below. As shown in FIG. 6, in the caseof the comparative example, the planar uniformity of the film thicknesson the three wafers were ±4.22%, ±3.88%, and ±4.54%, respectively. Onthe other hand, as shown in FIG. 7, in the case of the present example,the planar uniformity of the film thickness on the three wafers were±3.60%, ±2.76%, and ±2.79%, respectively. Accordingly, it has beenconfirmed that the planar uniformity of the film thickness can beimproved without reference to the height position of the wafers.

FIGS. 4 and 5 schematically show gas flows in these apparatuses. Asshown in FIG. 4, in the case of the comparative example, the major partof the process gas supplied from each of the gas distribution nozzles 34and 36 flows in the horizontal direction toward the wafers W, but smallparts thereof flow into the lower space S1 and upper space S2, asindicated by arrows 110A and 110B. These small parts may deteriorate theprocess throughput, the process gas usage rate, and the planaruniformity and/or inter-substrate uniformity of the process. In thiscase, since the lower space S2 has a volume far lager than the upperspace S2, the part of the process gas flowing into the lower space S2 ismore influential.

On the other hand, as shown in FIG. 5, in the case of the presentexample, the blocking gas is directly supplied to the lower space S1from the blocking gas nozzle 38, as indicated by an arrow 112A.Consequently, the process gas is inhibited from flowing into the lowerspace S1, thereby improving the problems described above to a largeextent. A nozzle structure for supplying the blocking gas to the upperspace S2 will be described later.

Experiments 2 and 3

Experiments were performed in the apparatus (present example) shown inFIG. 5, by use of different manners of supply of the blocking gas.Experiments 2 and 3 employed the same conditions as Experiment 1 exceptthat supply of the blocking gas was performed in different manners. InExperiment 2, supply of the blocking gas was performed in accordancewith the fourth example (C4) shown in FIG. 3, in which the N₂ gas usedas the blocking gas was set at a flow rate of 0.2 slm when the firstprocess gas containing DCS gas was supplied (the first step), and at 1slm when the second process gas containing NH₃ gas was supplied (thethird step). In Experiment 3, supply of the blocking gas was performedin accordance with the fifth example (C5) shown in FIG. 3, in which theN₂ gas used as the blocking gas was set at a flow rate of 1 slm when thefirst process gas containing DCS gas was supplied (the first step), andat 0.2 slm when the second process gas containing NH₃ gas was supplied(the third step).

FIGS. 8 and 9 are graphs showing the relationship between the positionon a wafer and the film thickness obtained by the apparatus shown inFIG. 5 in Experiments 2 and 3, respectively. In FIGS. 8 and 9, thehorizontal axis denotes the position (mm) on a wafer, and the verticalaxis denotes the film thickness (nm). No. 5, No. 31, and No. 57 in FIGS.8 and 9 denote the number of a wafer of 61 wafers supported on the waferboat 12, which were counted from below. As shown in FIGS. 8 and 9, theplanar uniformity and inter-substrate uniformity of the film thicknesswas greatly changed due to the different manners of supply of theblocking gas. Accordingly, it has been confirmed that the planaruniformity and inter-substrate uniformity of the film thickness can becontrolled by adjusting the flow rate of the blocking gas.

Second Embodiment

FIG. 10 is a sectional view showing a vertical plasma processingapparatus (vertical plasma film formation apparatus) according to asecond embodiment of the present invention. The apparatus shown in FIG.10 has the same structure as the apparatus shown in FIG. 1 except forthe arrangement concerning the blocking gas supply circuit 32. In theapparatus shown in FIG. 10, the blocking gas supply circuit 32 includesa gas nozzle 38X formed of a quartz pipe which penetrates the sidewallof the manifold 8 from the outside and then turns and extends upward.The distal end of the gas nozzle 38X extends beyond the top plate 12 bof the wafer boat 12 and reaches a position near the ceiling of theprocess container 4. The gas nozzle 38X has a gas spouting holes 38Blocated above the top plate 12 b of the wafer boat 12 and facing theupper space S2, which belongs to the marginal space. In this embodiment,supply of the blocking gas may be performed in accordance with selectedone of first to sixth examples (C1) to (C6) shown in FIG. 3.

Third Embodiment

FIG. 11 is a sectional view showing a vertical plasma processingapparatus (vertical plasma film formation apparatus) according to athird embodiment of the present invention. The apparatus shown in FIG.11 has the same structure as the apparatus shown in FIG. 1 except forthe arrangement concerning the blocking gas supply circuit 32. Also inthe apparatus shown in FIG. 11, the blocking gas supply circuit 32includes a gas nozzle 38Y formed of a quartz pipe which penetrates thesidewall of the manifold 8 from the outside and then turns and extendsupward, as in the apparatus shown in FIG. 10. The distal end of the gasnozzle 38Y extends beyond the top plate 12 b of the wafer boat 12 andreaches a position near the ceiling of the process container 4. The gasnozzle 38Y has gas spouting holes 38A and 38B respectively located belowthe bottom plate 12 a of the wafer boat 12 and above the top plate 12 bof the wafer boat 12 and respectively facing the lower space S1 andupper space S2, which belongs to the marginal space. Also in thisembodiment, supply of the blocking gas may be performed in accordancewith selected one of first to sixth examples (C1) to (C6) shown in FIG.3.

According to the third embodiment, the blocking gas is supplied to boththe lower space S1 and upper space S2, so that the process gas isinhibited from flowing into these spaces. Consequently, it is possibleto further improve the process throughput, the process gas usage rate,and the planar uniformity and/or inter-substrate uniformity of theprocess. In the third embodiment, two blocking gas nozzles may berespectively disposed exclusively for the lower space S1 and upper spaceS2 to supply the blocking gas therefrom to the respective spaces.

Modification

In the embodiments described above, the first process gas (containingDCS) that provides the main material of a thin film is not turned intoplasma, and the second process gas (containing NH₃) that reacts with thefirst process gas is turned into plasma. However, depending on the typeof CVD, only a gas that provides the main material of a thin film may beturned into plasma, or both of a gas that provides the main material ofa thin film and a gas that reacts with the former gas may be turned intoplasma.

In the embodiments, for example, the first process gas contains DCS gasas a silane family gas. In this respect, the silane family gas may beone or more gases selected from the group consisting of dichlorosilane(DCS), hexachlorodisilane (HCD), monosilane (SiH₄), disilane (Si₂Cl₆),hexamethyldisilazane (HMDS), tetrachlorosilane (TCS), disilylamine(DSA), trisilylamine (TSA), and bistertialbutylaminosilane (BTBAS).

In the embodiments, the second process gas contains ammonia (NH₃) gas asa nitriding gas. Where the present invention is applied to formation ofa silicon oxynitride film, an oxynitriding gas, such as dinitrogen oxide(N₂O) or nitrogen oxide (NO), may be used in place of the nitriding gas.Where the present invention is applied to formation of a silicon oxidefilm, an oxidizing gas, such as oxygen (O₂) or ozone (O₃), may be usedin place of the nitriding gas.

In addition to the process gases described above, an impurity gas, suchas BCl₃ gas, for introducing an impurity, and/or a carbon hydride gas,such as ethylene, for adding carbon may be further used. The presentinvention may be applied to another film formation process, such as aplasma CVD process, in place of the ALD process as described above.Further, the present invention may be applied to another plasma process,such as a plasma etching process, plasma oxidation/diffusion process, orplasma reformation process, in place of a plasma film formation processas described above. Further, the present invention may be applied toanother target substrate, such as a glass substrate or ceramicsubstrate, in place of a semiconductor wafer as described above.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method for forming a silicon-containing insulating film in avertical plasma processing apparatus for a semiconductor process, theapparatus comprising: a support member including a bottom plate and atop plate and configured to support a plurality of target substrates atintervals in a vertical direction; a process container configured toaccommodate the support member with the target substrates supportedthereon and having a process field, which has lower and upper endsdefined by the bottom and top plates of the support member,respectively, for processing the target substrates, and a marginal spaceout of the process field, which comprises one or both of a lower spaceand an upper space respectively present below the bottom plate and abovethe upper plate; a heater configured to heat the target substratesinside the process field; an exciting mechanism including a plasmageneration area disposed in a space communicating with the processfield, the plasma generation area extending over a length correspondingto the process field in a vertical direction; a process gas supplysystem configured to selectively supply into the process field a firstprocess gas containing a silicon-containing gas and a second process gascontaining a reactive gas selected from the group consisting ofnitriding gases, oxynitriding gases, and oxidizing gases, such that thefirst process gas is supplied into the process field not through theplasma generation area, and the second process gas is supplied into theprocess field through the plasma generation area, and the first andsecond process gases are supplied to form essentially horizontal gasflows in the process field over a length corresponding to the processfield in a vertical direction; a blocking gas supply circuit including ablocking gas supply port independent of the process gas supply systemand configured to directly supply a blocking gas comprising an inactivegas into the marginal space, the blocking gas supply port being locatedat a position on the same side as the exciting mechanism and opened tothe marginal space; and an exhaust system including an exhaust portdisposed at a position facing the plasma generation area with theprocess field interposed there between and configured to exhaust gasfrom the process field and thereby to exhaust the process gas and theblocking gas, the method being preset to deposit the silicon-containinginsulating film by repeating a process cycle a plurality of times, theprocess cycle alternately comprising: a first step of performing supplyof the first process gas to the process field while maintaining sshut-off state of supply of the second process gas to the process field;a second step of maintaining a shut off state of supply of the first andsecond process gases to the process field; a third step of performingsupply of the second process gas to the process field while maintaininga shut-off state of supply of the first process gas to the processfield, the third step including an excitation period of supplying thesecond process gas to the process field while exciting the secondprocess gas by the exciting mechanism, and a fourth step of maintaininga shut off state of supply of the first and second process gases to theprocess gases to the process field; wherein the process cycle comprisescontinuously exhausting gas from inside the process field through theexhaust port over the first, second, third, and fourth steps, andperforming supply of the blocking gas to the marginal space from theblocking gas supply port simultaneously with the supply of the first andsecond process gases to the process field in the first and third steps,respectively, to inhibit the first and second process gases from flowinginto the marginal space.
 2. The method according to claim 1, wherein theprocess cycle is arranged such that one of the first and second processgases is supplied at a smaller flow rate than the other of the first andsecond process gases is, and the blocking gas supplied simultaneouslywith said one of the first and process second process gases is suppliedat a larger flow rate than the blocking gas supplied simultaneously withsaid other of the first and second process gases is.
 3. The methodaccording to claim 2, wherein the first process gas is supplied at asmaller flow rate than the second process gas is.
 4. The methodaccording to claim 1, wherein the process cycle is arranged tocontinuously perform supply of the blocking gas to the marginal spacefrom the blocking gas supply port over the first, second, third andfourth steps.
 5. The method according to claim 1, wherein the processcycle is arranged to maintain a shut off state of supply of the blockinggas to the marginal space from the blocking gas supply port during eachof the second and fourth steps.
 6. The method according to claim 1,wherein the process cycle is arranged such that each of the second andfourth steps has a preceding period and a subsequent period whichrespectively perform and stop supply of the blocking gas to the marginalspace from the blocking gas supply port.
 7. The method according toclaim 1, wherein the exhaust port extends over a length corresponding tothe process field in a vertical direction.
 8. The method according toclaim 1, wherein the marginal space comprises the lower space, and theblocking gas supply port comprises a lower supply port opened to thelower space.
 9. The method according to claim 1, wherein the marginalspace comprises the lower space and the upper space, and the blockinggas supply port comprises a lower supply port and an upper supply portrespectively opened to the lower space and the upper space.
 10. Themethod according to claim 1, wherein the blocking gas comprises a gasselected from the group consisting of N₂, He, Ar, and Ne.
 11. The methodaccording to claim 1, wherein the silicon-containing gas comprises a gasselected from the group consisting of dichlorosilane (DCS),hexachlorodisilane (HCD), monosilane (SiH₄), disilane (Si₂Cl₆),hexamethyldisilazane (HMDS), tetrachlorosilane (TCS), disilylamine(DSA), trisilylamine (TSA), and bistertialbutylaminosilane (BTBAS). 12.The method according to claim 1, wherein the reactive gas comprises agas selected from the group consisting of ammonia (NH₃), dinitrogenoxide (N₂O), nitrogen oxide (NO), oxygen (O₂), and ozone (O₃).